To apply this theory to the RACP, this means that a car with a higher power output (higher stress) will theoretically fail sooner than an identical car of lower power output (lower stress). Fatigue life is dictated by the magnitude of the stress and the amount of cycles applied over time. The point at which fatigue failure occurs is known as the fatigue life. These cycle stresses are well below the strength limit of the material however, with time the sheet metal is progressively weakened and made more brittle to the point it fractures (cracks). Why do cracks occur?Ĭracks do not occur because the applied stresses (force over area) are simply so great that the steel tears but rather that the stresses are great enough to repeatedly flex (strain) the structure back and forth in cycles.
All E46 3-series models built roughly after Feb-2000 share the same Rear Axle Carrier Panel and there is no E46 entirely safe from ‘subframe cracks’.Īlthough, there is in fact some truth in the above that different models and years will fail differently and may need attention in areas that others do not however, we will come back to that later.īefore getting any further into the where’s and why’s, we feel it would be best to have a fundamental knowledge of fatigue related failure to help you the reader better understand why the E46 subframe mounts crack. Unfortunately, all of the above is technically incorrect.
There are common misconceptions that lead people to believe the issue isn’t universal to all E46’s such as convertibles having thicker floors, some models having additional or differently designed structures or that it only occurs in the earlier manufactured models not the later face-lift models. During this article we may change back and forth between RACP & subframe so sorry in advance if it causes some confusion. The common use term of ‘subframe cracks/failure’ is technically incorrect as it is not the subframe that cracks but rather the section of the chassis the rear subframe mounts to known as the Rear Axle Carrier Panel (RACP) although, the most frequent early sign of failure within the structure occurs at the subframe mounts themselves hence the terminology. No matter the shape, model or way it is driven, subframe cracks are inevitable. How the car is inspected and the safety precautions taken is at the discretion of the individual.ĭespite the beliefs of some, all E46 3-series BMW’s are prone to cracking at and around the rear subframe mounts. Be advised, CMP Auto Engineering is not liable for any damage to property or harm to yourself or others that occurs while inspecting your car. This article is intended to help those new to the E46 3-series chassis or not overly familiar with the rear subframe mount cracking issue.
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